The present invention relates to the art of functional neuromuscular stimulation. It finds particular application in providing hand control functions in central nervous system (CNS) disabilities such as quadraplegia and stroke victims and will be described with particular reference thereto. However, it is to be appreciated that the invention is also applicable to providing locomotive and control of other lower body functions in CNS disabled victims and to providing control of other muscles over which the patient has lost partial or full voluntary control.
In healthy humans, electrical signals originate in the brain and travel through the spinal cord and subsequently to peripheral nerves to a muscle which is to be contracted. More accurately, the signals travel to two or more muscles whose contractions apply forces antagonistically to a joint structure. The relative forces determine the degree and speed of movement. By appropriately applying the electrical stimulation to various muscles, a wide degree of voluntary movement can be achieved. In injuries to the CNS, the passage of electrical signals through the injured area may be disrupted. Commonly, lower spinal cord injuries will terminate the transmission of electrical control signals to muscles in the lower part of the body. Damage to the upper part of the spinal cord may block the flow of voluntary muscular control signals to upper and lower body regions. For example, in an upper spinal column injury at the C6 vertebrae, which is frequently injured in accident victims, muscular control below the elbows is commonly lost.
As early as 1791, Luigi Galvani produced artificial contractions in the muscle of frogs"" legs by the application of electrical potentials. In the ensuing years, electrical stimulation therapy has been greatly refined. Cardiac pacemakers, for example, have become commonplace.
Several different groups of researchers have enabled paraplegic patients to stand and walk with walkers or crutches by applying preselected sequences to surface electrodes over their leg muscles. Surface stimulation is satisfactory for some walking and other less detailed movements. However, with surface electrodes, it is difficult to make an accurate selection of the muscle to be stimulated or an accurate prediction of the strength of the stimulus signal reaching the muscle.
Surgically implanted electrodes provide accurate selection of the muscle to be stimulated. Further, the stimulation remains more consistent over a long period of time. This renders implanted electrodes advantageous for the more delicate and complex motion associated with the hands.
Numerous experimental systems have been devised and implemented to provide computer controlled electrical stimulation to the muscles of the legs, arms, and hands of patients. These experimental systems are commonly large and bulky. Frequently, the patient must be connected with a personal computer or other small computer by a cable or tether. Although smaller, dedicated computer systems could be designed, the larger programmable computer systems are generally preferred for experimental flexibility. The response to a given stimulus varies widely among patients and over time within each patient. The larger programmable computer facilitates customizing for different patients and changes in a given patient.
The present invention provides a new and improved functional neuromuscular stimulation system which increases patient independence and performance.
In accordance with one aspect of the present invention, a functional neuromuscular stimulation system is provided. An input command means provides a command control signal which is indicative of a selected physiological movement or group of movements. A first parameter processing means derives the parameters of a first parameter processing means includes an amplitude means for selecting an amplitude of each stimulation pulse of the pulse train, an interval means selects an interpulse interval between pulses of the pulse train and a pulse width means selects a pulse width for each pulse of the pulse train, each in accordance with the control signal. A pulse train generator generates a pulse train with the selected amplitude, interpulse interval, and pulse width. An electrode is connected with the pulse train generator for applying the pulse train to a muscle to be stimulated.
In accordance with a more limited aspect of the present invention, a plurality of similar parameter processing means are provided for uniquely deriving additional stimulation of pulse trains from the control signal(s) for application to additional electrodes implanted at other locations in the same or other muscles.
In accordance with another more limited aspect of the present invention, a physiological parameter monitor is provided for monitoring a preselected parameter of physiological movement, such as position or force. A parameter comparing means compares the monitored parameter with a parameter value retrieved from a preprogrammed look-up table. Any difference between the monitored and retrieved parameters is determined. At least one of the amplitude, interpulse interval, and the pulse width of the stimulus pulse train are adjusted such that the difference is minimized.
In accordance with another aspect of the present invention, a Hall-effect command control signal generator is provided. A permanent magnet is mounted in a ball member, such as in an externally worn device or surgically implanted, e.g. in the clavical of the patient. A first pair of Hall-effect plates are mounted in a socket member, such as external device or the sternum of the patient to define an axis. At least one additional Hall-effect plate is mounted in the socket member to define a second axis. A power supply provides a current flow in one direction across each of the Hall-effect plates. A potential difference monitoring means monitors the potential difference generally transverse to the first direction across each Hall-effect plate to provide an output signal indicative of the change of potential thereacross. In this manner, as the permanent magnet moves relative to the Hall-effect plates, the change in their relative proximity causing corresponding changes in the magnetic flux density across each plate which causes corresponding changes in the path of current flow along said one direction, hence the potential difference across the Hall-effect plates. In this manner, the output signals from the potential difference monitoring means are indicative of the angular position of the ball and socket member relative to the first and second axes.
In accordance with another aspect of the invention, a joystick includes a ferrite core mounted in a ball member. The ball member is rotatably mounted in a socket member. A driving coil is connected with the socket member encircling at least a portion of the ferrite core. A plurality of sensing coils are mounted to the socket member adjacent the ferrite core such that the transfer of an input signal from the driving coil to each of the sensing coils is controlled by the relative proximity between the ferrite core and the sensing coils.
In accordance with another aspect of the invention an implanted telemetry system is provided. An antenna receives a radio frequency signal which is converted into electromotive power by a power supply. An encoding means encodes an electrical signal which controls a gate means. The gate means selectively connects a load across the antenna to modulate a characteristic thereof such that a monitorable characteristic of the radio frequency signal is also modulated by the load.
In accordance with another aspect of the present invention, a laboratory system customizes electrical stimulus pulses to the patient. The system includes a command processing means for providing control parameters indicative of selected command functions and degrees of movement. A movement planning means derives movement parameters indicative of preselected movement, force, or other motion related parameters of the controlled limb in response to each control parameter. A coordination and regulation means derives appropriate stimulus parameters from the motion parameters. A stimulus generator assembles an appropriate electrical stimulus pulse train in accordance with the stimulus parameters.
In accordance with a more limited aspect of the present invention, a comparing means is provided for comparing actual physical motion parameters achieved by the patient""s limb being controlled and the selected motion parameters of the movement planning means. The stimulus parameters selected by the coordination regulation means are automatically adjusted in order to bring the actual and selected motion parameters into optimal coincidence.
In accordance with another aspect of the present invention, a multichannel implanted stimulator system is provided. The stimulator system includes an antenna for receiving a carrier signal which is modulated with channel, pulse width, and pulse amplitude information for one or more of the channels. A power supply means derives operating voltage for other system components from the carrier signal. A decoding means decodes at least selected channel, pulse width, and pulse amplitude information from the modulations. For each channel, an energy storage means is provided for providing energy for a current pulse from the power supply through the muscle tissue between a stimulating electrode and a reference electrode. A channel selection means selects the appropriate channel and corresponding stimulating electrode to which an electrical pulse of the decoded pulse width is to applied. A current regulating means regulates the amplitude of the pulse in accordance with the decoded amplitude.
In accordance with another aspect of the invention, the implanted stimulus system includes a metal capsule which defines a hermetically sealed chamber therein. A receiving antenna receives signals indicative of the stimuli to be applied to electrodes. Electrical circuitry is mounted in the capsule for converting received radio frequency signals into stimulus pulses. A plurality of electrical leads are electrically connected with the circuitry and the electrodes and mechanically connected with the capsule.
In accordance with another aspect of the invention, an electrical lead construction for implanted electrodes is provided. First and second lengths of multi-strand wire are wrapped helically around a longitudinal axis of the lead. A flexible polymeric insulator material encapsulates the helically wound wires.
In accordance with another aspect of the present invention, a shield assembly is provided for protecting a percutaneous interface. A shield member includes a peripheral lip portion extending peripherally around a central shield member portion. The central shield member portion is constructed of a resilient elastomeric material with a low profile. An aperture is defined through the central shield member for alignment with a point at which electrical wires pass through the patient""s skin. An electrical connector which is operatively connected with the electrical lead wires passing through the patient""s skin is mounted to the shield member central section. An overlay member having an aperture which conforms with the shield member central portion overlays the shield member and is adhesively adhered to the shield member peripheral lip portion and to the patient""s skin around the shield member.
One advantage of the present invention is that it is readily customized to an individual patient. Moreover, the customization can be altered and refined as the patient becomes more proficient with the apparatus, as the patient""s muscles become stronger, and the like.
Another advantage of the present invention resides in its portability.
Yet, another advantage of the present invention resides in the ease with which operators can adapt it to an individual patient.